The invention relates to a paper for thermal image transfer to flat porous surfaces, such as textiles.
Various processes exist which enable individual, personalized images or motifs to be transferred to textiles.
One of these processes is disclosed in DE-OS 26 53 654 which relates to the creation on cloth of long-life xerographically produced images. The problem is solved by the production of a silicone-coated web having disposed thereon a cover layer on which the image is produced xerographically. The toner image on the cover layer can be further transferred to the textile material within 30 seconds by the action of heat and pressure in a laminating press at approximately 180.degree. C.
One disadvantage of that transfer paper is the silicone coating. When after image transfer the silicone-coated paper is drawn off the textile backing, silicone residues remain sticking to the fibres of the backing. Furthermore, the images transferred to the textile material have unsatisfactory wash-fastness.
EP 0 479 882 discloses a process and the associated transfer paper for transferring motifs to a porous backing wherein the paper consists of a coated paper support containing a polyethylene layer. The images to be transferred are printed on the paper by dry copying and then transferred to the textile backing by the action of heat and pressure.
One disadvantage of the transfer paper is the unsatisfactory color density of the images transferred to the backing by means of said paper.
EP 0 466 503 A1 discloses an image carrier sheet for use in an image transfer process wherein the carrier sheet comprises a flexible web base and two layers formed thereon. One surface layer, which is directly formed on the web consist of an polymeric material, and the second layer, which is formed on the first layer, is a thermoplastic coating. For image transfer the thermoplastic coating is transferred to the textile substrate and the flexible web together with the polymeric layer is drawn off.
It is an object of the invention to develop a paper by means of which xerographically produced toner images or images produced by thermal processes can be transferred with high color density and resolution to flat porous surfaces, more particularly textile backings.
This problem is solved by a paper which is characterized by a paper support and a layer applied thereto which contains an ethylene copolymer or an ethylene copolymer mixture and a dye-receiving layer.
More particularly the copolymer contains 10 to 35 mol % of another monomer.
The ethylene copolymer can more particularly be an ethylene-vinyl acetate copolymer or an ethylene-(meth)acrylic acid alkyl ester copolymer. However, a mixture of said copolymers can also be used.
In the particular embodiment of the invention the ethylene copolymer has a vinyl acetate or (meth)acrylic acid alkyl ester content of 10 to 35 mol%.
The ethylene/(meth)acrylic acid alkyl ester-copolymer can be selected from the group formed by the following copolymers:
Ethylene/methyl(meth)acrylate, ethylene/ethyl(meth)acrylate, ethylene/propyl(meth)acrylate, ethylene/n-butyl(meth)acrylate or ethylene/isobutyl(meth)acrylate and also mixtures thereof.
The layer containing the ethylene copolymer is extruded on to a paper support. The coating weight of the layer is 10 to 50 g/m.sup.2. Prior to the extrusion coating, the surface of the paper is subjected to a corona discharge.
Any paper can be used as the paper support, but a high-sized neutral basic paper having a base weight of 60 to 200 g/m.sup.2 is more particularly suitable. The base paper can be surface sized with starch or polyvinyl alcohol and has on both sides a surface smoothness of 20 to 300 Bekk.
The dye-receiving layer applied to the layer containing an ethylene copolymer contains a polymer of low film forming temperature.
The polymer can be more particularly an acrylic acid ester copolymer, a styrene/butadiene or an acrylonitrile butadiene-latex. However, it is also possible to use other polymers which have a good affinity with the dye or toners used for printing.
In another embodiment of the invention the dye-receiving layer can also contain an antiadhesive agent. Finely dispersed silicas, more particularly an aluminium-doped finely dispersed silica are particularly suitable for this purpose.
The paper quality may further be improved in view of the ability to be pitted up and with view to a regular undisturbed passage during the reproduction onto the paper, when the dye-receiving layer additionally contains inorganic and/or organic pigments.
Particularly preferred are hollow or other resin particles on the basis of styrene resins as polystyrene or on the basis of acrylic resins as polymethyl(meth)acrylate or styrene/acrylic acid alkylester-copolymers. Starch is well suited and has to be regarded as pigment, because it is directly admixed to the coating solution and suspended therein.
Suitable inorganic pigments are TiO.sub.2, CaCO.sub.3, ZnO, ZnS, ZnSO.sub.4, Sb.sub.2 O.sub.3, CaSO.sub.4, kaolin, talcum or mixtures thereof.
The amount of the pigment in the dye receiving layer is between 10 to 90 wt %, preferably 30 to 70 wt %, based on the dry layer.
The above mentioned improved properties are evaluated by determining a friction coefficient with a tractive force testing apparatus according to the Frank principle.
Use of pigments in the dye receiving layer results in friction coefficients of less than 4N. The friction coefficient is the force which is required to dislocate the back side of a sheet compared to its front side.
The dye-receiving layer is applied from an aqueous coating solution. All the usual application and metering methods can be used for this purpose. The coating weight of the dye-receiving layer is 0.1 to 0.5 g/m.sup.2.
Non-impact methods such as, for example, laser printers and laser copiers can be used to print on the surface of the paper according to the invention any desired motif, which can then be transferred to all synthetic or natural fabrics, but also to other flat articles. To this end the paper bearing a motif is brought into contact with a flat backing. The transfer is performed by the action of heat (130.degree.-180.degree. C.) and pressure (34.5.times.10.sup.4 N/m.sup.2), and only the paper support is thereafter drawn off the backing. The transferred image penetrates completely into the fibres of the backing.
In comparison with the conventional transfer papers or those disclosed by the prior art, the following advantages may be mentioned:
increased brilliance of color (improved color reproduction); PA1 uniform trouble-free flow during reproduction on the paper according to the invention; PA1 improved stackability; PA1 wash-fastness of the transferred image on the textile material; PA1 complete separation of the printed layer, without residues on the paper drawn off; PA1 environmentally acceptable image transfer, since after removal only the uncoated paper support is left.